Transposable elements (TEs) and DNA repeats are commonly targeted by DNA and histone methylation to achieve epigenetic gene silencing. We isolated mutations in two Arabidopsis genes, AtMORC1 and AtMORC6, which cause de-repression of DNA-methylated genes and TEs, but no losses of DNA or histone methylation. AtMORC1 and AtMORC6 are members of the conserved Microrchidia (MORC) adenosine triphosphatase (ATPase) family, predicted to catalyze alterations in chromosome superstructure. The atmorc1 and atmorc6 mutants show decondensation of pericentromeric heterochromatin, increased interaction of pericentromeric regions with the rest of the genome, and transcriptional defects that are largely restricted to loci residing in pericentromeric regions. Knockdown of the single MORC homolog in Caenorhabditis elegans also impairs transgene silencing. We propose that the MORC ATPases are conserved regulators of gene silencing in eukaryotes.

We studied weekly and bimonthly survival of select nongame fishes that were implanted with 8‐mm PIT tags in upper Piedmont streams of South Carolina, USA. Weekly survival in stream enclosures was assessed for a total of 350 tagged individuals and 311 control (untagged) fish (39–101 mm TL; median = 65 mm TL) belonging to six species (Bluehead Chub Nocomis leptocephalus, Creek Chub Semotilus atromaculatus, Yellowfin Shiner Notropis lutipinnis, Mottled Sculpin Cottus bairdii, Northern Hog Sucker Hypentelium nigricans, and Striped Jumprock Moxostoma rupiscartes). Weekly survival rates ranged from 93.3% to 100% among species, with Yellowfin Shiners experiencing the lowest survival rate. Only 2 of the 337 surviving tagged individuals lost their tags (0.6% tag loss). Logistic regression indicated that species and body length were statistically significant predictors of survival and tag retention. Odds ratios indicated that tagged fish were 1.718 times less likely to survive than control fish, but the tagging effect was not statistically significant. Bimonthly survival was estimated by conducting a mark–recapture study from September 2015 to May 2016, which involved tagging 1,413 unique individuals of Bluehead Chub (45–75 mm TL) in a 520‐m stream section and 431 individuals of Mottled Sculpin (45–75 mm) in another 740‐m section. Bayesian state–space analysis of Cormack–Jolly–Seber models indicated that apparent survival did not differ between newly tagged and previously tagged (i.e., recaptured) individuals in any sampling interval, suggesting that the acute and chronic effects of tagging did not differ. Mean bimonthly apparent survival rate was 0.76 (95% credible interval = 0.64–0.86) for Bluehead Chub and 0.74 (95% credible interval = 0.59–0.88) for Mottled Sculpin. Our results indicate that PIT tags can be successfully applied to study the ecology and life history of small‐bodied, nongame fish species, although caution should be exercised when selecting the species and body sizes to be tagged.

Passive integrated transponder (PIT) tags have been used to infer demography and behavior of lotic fishes, but their application has mostly been limited to salmonids. We studied the efficiency of a portable PIT antenna in a small Piedmont stream (mean width = 2.4 m) in South Carolina by comparing two tag sizes (8‐ and 12‐mm full‐duplex tags) applied to two nongame species (Mottled Sculpin Cottus bairdii and Creek Chub Semotilus atromaculatus). A 285‐m stream reach was blocked off under base flow conditions in September 2016, and 8‐ or 12‐mm PIT tags were implanted in 67 Creek Chub (62–138 mm TL) and 65 Mottled Sculpin (60–88 mm TL). Starting at 1 d after tagging, the study reach was sampled with the portable PIT antenna twice daily for five consecutive days, during which apparent survival of tagged fish was assumed. Generalized linear mixed‐effects models with a logistic link identified that detection efficiency depended on species, tag size, body length, and the species × body length interaction. Mottled Sculpin had detection rates of 56% (8‐mm tags) and 79% (12‐mm tags), with 67% of detections occurring in riffle‐dominated sections, whereas Creek Chub had 3% (8‐mm tags) and 16% (12‐mm tags) detection rates, with 62% of detections occurring in pool‐dominated sections. Detection efficiency decreased with body size in Creek Chub but not in Mottled Sculpin; the observed decrease for Creek Chub was most likely attributable to an ontogenetic habitat shift. The reasonably high detection efficiency of Mottled Sculpin, even with 8‐mm tags, suggested that the portable PIT antenna can be a viable option for some species in small streams, allowing individual‐based approaches to studying small‐bodied species or earlier life stages without the need for repeated physical capture and handling. Received May 13, 2017; accepted October 2, 2017Published online November 10, 2017